1. Field of the Invention
The present invention relates to a two-stroke operable hand air pump that may pump air during every stroke of the piston.
2. Description of the Related Art
A conventional air pump may output air in an output stroke only such that the user is exhausted very soon. A two-stroke operable pump has been proposed to output air during every stroke of the piston. Two sealing rings each having an annularly extending conic lip are respectively mounted in two annular grooves of the piston such that the conic lips face each other. The lips are in sealing contact with an inner periphery of a cylinder. In addition, each lip is deformable toward the piston rod to allow passage of air, thereby allowing output of air during each stroke of the piston. It is, however, found that, air tends to leak in the lip portion, as the lip that is compressed by high pressure air is hollow. Applicant's U.S. patent application Ser. No. 09/211,120 discloses improved two-stroke operable pumps that successfully solve this problem. The present invention provides different designs in this regard.